Low leakage rate composite gasket

Abstract

A gasket comprising a first discrete component and a second discrete component, wherein the first and second components extend along the length of the gasket. The second component is arranged ranged relative to the first component so as to separate the first component at least from one of the two sealing surfaces. The first component is relatively hard in at least the thickness direction of the gasket and preferably incompressible and the second component is relatively soft in at least the thickness direction of the gasket and compressible. When the gasket is compressed between two flanges, there is a limited region of high compression, because the first component increases the pressure by which the second component is compressed between the surfaces of the flanges. This yields a high leak tightness of the sealing at a relatively low force.

What is claimed is: 
     
       1. A gasket having a thickness between two sealing surfaces and further having a length and a width, the width being at least 1.5 times as large as the thickness, said gasket comprising a first discrete component and a second discrete component, the first and second components extending along the length of the gasket and the second component being arranged relative to the first component so as to separate the first component at least from one of the two sealing surfaces at a discrete sealing area, wherein
 the first component is substantially impermeable for gas and liquids in at least the width direction of the gasket, 
 the second component is a porous fluoropolymer compressible in at least the thickness direction of the gasket, the Shore A hardness of the first component in the thickness direction being greater than the Shore A hardness of the second component in the thickness direction by a factor in the range of 1.5 to 2.5, wherein the Shore A hardness of the first component is in the range of 60 to 100 Shore A, 
 the first component or a section of increased thickness thereof, as compared to its average thickness, extending along the length of the gasket has a width that is less than 50% of the width of the second component, and 
 wherein, upon compression of said gasket over its entire width with an average pressure of 10 MPa, said second discrete component has a first density at said discrete sealing that is at least 1.25 times as great as a second density not in said discrete sealing area. 
 
     
     
       2. The gasket according to  claim 1 , wherein the width of the first component or section of increased thickness thereof is less than 30%. 
     
     
       3. The gasket according to  claim 1 , wherein the Shore A hardness of the second component is in the range of 30 to 70 Shore A. 
     
     
       4. The gasket according to  claim 1 , wherein a density of the first component is at least 50% of its theoretical density. 
     
     
       5. The gasket according to  claim 1 , wherein the density of the first component is greater than the density of the second component by a factor in the range of 1.5 to 6. 
     
     
       6. The gasket according to  claim 1 , wherein the first component comprises an expanded fluoropolymer. 
     
     
       7. The gasket according to  claim 1 , wherein the second component comprises expanded fluoropolymer. 
     
     
       8. The gasket according to  claim 1 , wherein the first component has a hollow cross section and/or is made from a porous material having a closed cell pore structure. 
     
     
       9. The gasket according to  claim 1 , wherein the second component comprises at least one layer formed of a stack of uniaxially or biaxially expanded membranes, the direction of expansion being different to the length and width directions of the gasket. 
     
     
       10. The gasket according to  claim 1 , wherein the gasket comprises at least one further component, the hardness of the further component being lower than the hardness of the relatively hard first component. 
     
     
       11. The gasket according to  claim 1 , wherein the gasket comprises two or more first components.